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The discovery of feathers in a fossil that predates most birdlike dinosaurs has calls into serious question the idea that birds descended from dinosaurs.

Researchers writing in today's issue of Science made the discovery while painstakingly examining a specimen only chanced upon at a recent touring exhibit of Russian fossils.

"These are some amazing fossils, and at the very least they prove that feathers did not evolve in dinosaurs," said John Ruben, Professor of Zoology at Oregon State University (OSU). "The supposed link between dinosaurs and birds is pretty entrenched in palaeontology, but it's not as solid as the public has been led to believe."

The fossils are of a small reptile called Longisquama insignis which researchers say glided between trees in central Asia 220 million years ago. The oldest animal prior to this that everyone agrees was a feathered bird is called Archaeopteryx, which first appears in the fossil record about 75 million years later. It has been a huge mystery where the feathers of Archaeopteryx evolved from, and many experts had theorised they were linked to dinosaurs.

"A point that too many people always ignored, however, is that the most birdlike of the dinosaurs, such as Bambiraptor and Velociraptor, lived 70 million years after the earliest bird, Archaeopteryx," said Ruben. "So you have birds flying before the evolution of the first birdlike dinosaurs. We now question very strongly whether there were any feathered dinosaurs at all. What have been called feathered dinosaurs were probably flightless birds."

On the other hand, Ruben said, Longisquama would have lived in the right time, and had the right physical structure, to have been the distant evolutionary ancestor of birds.

While the fossil evidence examined in this study does not conclusively prove that this animal was indeed the ancestor of flying birds, Ruben said, it's clearly consistent with that possibility.

"We can identify certain structures in these fossils that you only find in feathers and just don't see anywhere else," said Terry Jones, also an OSU paleontologist and co-author on the study. "So we're quite sure we're looking at the earliest feather. But beyond that, this animal looks like an ancestral bird even if you ignore the feathers. The teeth, pectoral structure, neck, and skull are just like those of birds."